Composite materials offer potential design improvements in gas turbine engines. For example, in recent years composite materials have been replacing metals in gas turbine engine fan blades because of their high strength and low weight. Most legacy gas turbine engine fan blades are titanium with a thin cross-section. The ductility of titanium fan blades enables the fan to ingest a bird and remain operable or be safely shut down. The thin cross-section allows high levels of aerodynamic efficiency. The same requirements are present for composite fan blades.
A composite airfoil has a root, which connects to the fan mechanism, and a tip opposite the root. A composite airfoil for a turbine engine fan blade is typically designed with a divergent root portion known as a dovetail root. The thickness of the airfoil greatly changes over the length from the tip to the root. This is due to various strength and stiffness requirements in various locations of the airfoil to optimize the performance of the airfoil under various conditions, including a bird strike.
Traditionally the composite fan blade is a two-dimensional laminate fan blade made of many layers of composite material. A composite fan blade can also be made of a three-dimensionally woven preform. Often a sheath is placed over the leading edge of the blade to protect the blade against erosion and damage from the strike of a foreign object, such as a bird.